1. Field of the Invention
The present invention relates to the assembly of statically indeterminate prefabricated pre-stressed reinforced concrete elements.
2. Description of the Prior Art
Australian Patent No. 155,756 granted to Stressteel for "Reinforced concrete constructions utilizing jointed reinforcement under tension" shows an apparatus for prestressing reinforcements or for adding important stresses to pre-stressed reinforcements. The stresses are applied uniformly to all the reinforcements which are prevented from bonding to the concrete by means of tar or like. The stressing device comprises an auxiliary hydraulic assembly and a cage fixed to the reinforcements by means of nuts, outside the cage; split washers, preventing the nuts from crushing the concrete are removed after the stressing has been carried out.
U.S. Pat. No. 3,405,490 granted to Robert R. La Marr for "Anchor structure for post-tensioned tendons" describes a button-head type tensioning assembly for reinforcements in concrete elements. Button-heads-formed on the opposite ends of the reinforcements are received in soft bushings placed in sockets located in slots formed in dead-end plates disposed at opposite portions of the concrete member. Upon applying tension to the tendons, by means of a nut-and-collar type apparatus, the heads are compressed into the bores of the bushings, thereby expanding the bushing and locking it in the associated socket. Here again, the reinforcements are prevented from bonding to the concrete. U.S. Pat. No. 3,387,417 granted to Howlett for "Prestressing Apparatus" describes an apparatus for coupling reinforced concrete elements while stressing the reinforcements. An externally threaded tubular sleeve is concentrically mounted on the spliced reinforcements which terminate with a button head and is secured to plate embedded in concrete. A coupling cage having an internally threaded bore engages with the sleeve member. Several sleeves may engage with one cage, thus allowing coupling of concrete elements having reinforcements of different diameters and of concrete elements having different numbers of reinforcements. External jacking means are applied for tensioning the reinforcements.
It is also common practice to weld together the iron rods projecting from the elements and to complete the joints by cementing them. Such a procedure, however, is slow and cumbersome, and does not allow for any standardization of the ends of the elements to be assembled.
A device has also been proposed to ensure the transmission of tensile stresses between reinforcements by means of conical anchorages. This system, however, has the disadvantage that the cones gradually sink in, causing a loss of tension, and that they do not permit adjustment of the traction between the reinforcements. Another suggestion was for systems which enabled the reinforcements to be joined without allowing the reinforcement to be subjected to stresses before the prefabricated elements were placed in position or the stresses at right angles to the joints to be adjusted. Finally, assembly devices have been proposed in my U.S. Pat. No. 3,665,665 granted May 30, 1972 for "Assembly of Concrete Support Elements", using the same part according to whether the joint is girder to girder, girder on upright or girder with girder on upright, the fitting operation consisting merely of tightening bolts. But the elements to be assembled had a joint plane bisecting the angle between the longitudinal axes of the elements. This method resulted in a marked simplification and standardization of the assembly operations, but its applications remain limited.